First open your terminal & Type following command
use auxiliary/gather/search_email_collector show options
The next step you need to set up the domain you want to locate the email address.
When we finished setup the domain, the default searching engine that will be use for this searching are Google, Bing, and Yahoo.
Now next step is type
set domain “name of domain” (without quote) & press enter.
& type run and press enter.
It will search email address of domain in google,yahoo & bing.